Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes for labeling human cancer cells

Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes proceed with rate constants up to 3.38 +/- 0.31 M-1 s(-1) in CD3CN, or 59 times faster than the analogous reaction of azides. This highly specific modular labeling strategy can be applied for direct labeling of proteins and for live cell imaging of cancer cells.